Methods and apparatus for procuring formation samples from well bores



June 30, 1970 J R G058 3,517,756

METHOD AND APPARATUS FOR PROGURING FORMATION SAMPLES FROM WELL BORESFiled 001;. 25, 1968 z/Zrck R 60;:

INVENTOR.

United States Patent METHODS AND APPARATUS FOR PROCURING FORMATIONSAMPLES FROM WELL BORES Jack P. Goss, Lake Charles, La., assignor toSchlumberger Technology Corporation, New York, N.Y., a corporation ofTexas Filed Oct. 23, 1968, Ser. No. 769,790 Int. Cl. E21b 49/04 US. Cl.175-4 15 Claims ABSTRACT OF THE DISCLOSURE In accordance with the newand improved methods disclosed herein, a coring bullet is impelled intoan earth formation with sufiicient force to drive a columnar samplethereof into the axial bore of the bullet. To retract the bullet fromthe formation, it is at least partially rotated and, preferablysimultaneously therewith, pulled in a generally-rearward direction awayfrom the formation. A preferred embodiment of the invention is providedby connecting two flexible cables of unequal length between a suitabletool and circumferentially-spaced points on each coring bullet so thatlongitudinal movement of the tool will initially tighten the shortercable and twist the bullet about its longitudinal axis as it is beingpulled rearwardly. When the longer cable is subsequently tightened bycontinued movement of the tool body, an added pull will be imparted tothe bullet to complete its withdrawal.

It is, of course, quite common to obtain samples of earth formationstraversed by a borehole by means of any one of a variety of so-calledcoring bullets. Such sample-taking or coring bullets are typicallycomprised of a tubular body having an open axial bore adapted to receiveformation materials cut away by a hardened cutting edge on theforwardmost portion of the body. In the usual situation, these coringbullets are respectively mounted in lateral chambers spacedlongitudinally along a suitable tool body adapted for suspension in aborehole. Explosive charges are disposed in each of the bullet chambersso that, upon detonation, the coring bullets will be explosivelyimpelled into the face of an adjacent earth formation with suflicientforce to drive a generallycolumnar formation sample or core into theaxial bore of each bullet. One or more flexible cables or tethers areusually used to securely connect each bullet to the tool body so that,after the bullets have been fired, they will be withdrawn from theformation as the tool is retrieved. Thus, whatever formation materialshave been captured by the bullets may be recovered at the surface forexamination and testing.

Although coring bullets of this nature are usually quite effective, itis not at all uncommon for a small, but still significant, number ofthese bullets to be left behind when the tool is retrieved. Inparticular, it has been observed that the loss of bullets seems to bemore common in the harder earth formations. As a result, it is generallybelieved that those bullets which are lost are so tightly embedded in ahard formation that their respective connecting cables will fail beforea sufiicient amount of the formation immediately surrounding the bulletscan be torn away to free the bullets.

Accordingly, it is an object of the present invention to provide new andimproved methods and apparatus for more reliably obtaining samples ofearth formations. This and other objects of the present invention areattained by impelling a typical core-taking bullet into the exposed faceof an earth formation. Then, once the bul- 3,51 7,7 56 Patented June 30,1970 "ice let has been at least partially embedded into the earthformation, the bullet is withdrawn therefrom by conjunetively rotatingit about its longitudinal axis as a retracting force is being appliedthereto. In the preferred manner of imparting these rotative andretractingforces to a typical coring bullet, two flexible tethers ofunequal length are respectively connected between the tool body carryingthe bullet and circumferentially-spaced portions of the bullet. Thus, asthe tool body is progressively displaced in relation to the embeddedbullet, the shorter tether will first be tightened to angularly rotatethe bullet about its longitudinal axis as well as to apply a reverselydirected retracting force thereto. Then, if necessary, continueddisplacement of the tool body will tighten the longer tether so that thetwo tethers will ultimately both apply reversely-directed retractingforces to the bullet to complete its withdrawal from the earthformation.

The novel features of the present invention are set forth withparticularity in the appended claims. The invention, together withfurther objects and advantages thereof, may be best understood by way ofthe following description of exemplary apparatus and methods employingthe principles of the invention as illustrated in the accompanyingdrawings, in which:

FIG. 1 depicts a typical sidewall coring tool in which a preferredembodiment of new and improved apparatus has been provided forpracticing the method of the present invention;

FIG. 2 is a cross-sectional view of the illustrated coring tool takenalong the lines 2 of FIG. 1; and

FIG. 3 is a fragmentary isometric view of the tool shown in thepreceding drawings as the present invention is being practiced.

Turning now to FIGS. 1-3, sidewall sample-taking apparatus 10incorporating the principles of the present invention is shown suspendedfrom a typical suspension cable 11 in a borehole 12 and adjacent anearth formation 13 from which one or more sample cores are desired. Asis typical, the sample-taking apparatus 10 includes an elongated body 14having a plurality of longitudinally-spaced lateral chambers 15respectively receiving the base of a typical coring bullet 16 such as,for example, any of those shown in Pat. No. 3,072,202, Pat. Nos.3,220,490 through 3,220,493 or in Pat. No. 3,329,- 217. O-rings 17around the rearward portions of the bullets 16 fluidly seal a smallcharge of a propellant explosive as at 18 in each lateral chamber 15behind the rear or base portion of each coring bullet. Anelectrically-responsive igniter, as at 19, is operatively inserted intoeach chamber 15 and connected to conductors in the cable 11 forselectively detonating the explosive charges 18. Inasmuch as thesample-taking apparatus 10 as has been described so far is typical, itis believed unnecessary to devote further attention to its description.

When it is desired to obtain one or more core samples from the earthformation 13, the tool 10 is positioned in the usual fashion in theborehole 12 immediately adjacent to the formation. One or more of theigniters 19 are then selectively energized from a power source (notshown) at the surface to impel a corresponding number of the bullets 16into the exposed face of the formation 13 for procuring a desired numberof formation cores.

As previously mentioned, the nose portions of the coring bullets 16 willbe at least partially embedded in the earth formation 13, with the depthof their penetration, of course, being governed by the character of theformation. Generally speaking, however, for a given type of bullet andquantity of explosive 18, the bullet 16 will be more deeply embedded ina softer formation than in a harder formation. In any event, withdrawalof the bullet 3 12516 generally requires a substantialrearwardly-directed orce.

Accordingly, in accordance with the present invention, withdrawal ofeach of the bullets 16 is more reliably accomplished than has beenpossible heretofore by at least partially rotating the bullet about itslongitudinal axis and, preferably simultaneously therewith, pulling onthe bullet in a generally-rearward direction with sufiicient force toretract it from the formation 13. It will be appreciated, therefore,that by conjunctively rotating each bullet 16 about its longitudinalaxis as it is being retracted, the force required to withdraw the bulletwill be less than that required by simply pulling the bullet out of theformation.

Although various devices can, of course, be devised for accomplishingthe joint rotation and retraction of the bullets 16, the preferredembodiment of the apparatus for accomplishing this is best illustratedin FIG. 3. As seen there, the bullet 16 has been propelled into theformation not shown in FIG. 3) to obtain a core sample 20. To connectthe bullet 16 to the tool body 14, flexible cables or tethers 21 and 22are secured in the usual fashion to opposite sides of the bullet andrespectively connected at their opposite ends to the tool body. Thetethers 21 and 22 are, of course, of sufficient length to allow thebullet 16 to be propelled out of the chamber and travel a shortpredetermined distance before the tethers are fully extended. As istypical, recesses or grooves 23 and 24 are arranged along the tool body14 on opposite sides of the chamber 15 to respectively receive thetethers 21 and 22 which, for convenience, are usually neatly coiled (asbest shown in FIG. 2) in these grooves so as to be smoothly payed out asthe bullet 16 is propelled out of the chamber.

Instead of employing tethering cables of equal length as has beentypical heretofore, in the present invention the tethers 21 and 22 areof unequal lengths. Accordingly, as depicted in FIG. 3, to withdraw thebullet 16, it is necessary only to either lower or (as shown by thearrow 25) raise the tool body 14. In this manner, such longitudinalmovement of the tool 10 will first tighten the shorter tether 21 tobegin rotating the bullet 16 (as shown by arrow 26) about itslongitudinal axis 27 and, either simultaneously or shortly thereafter,begin pulling the bullet rearwardly (as shown by the arrow 28). Then,upon continued longitudinal movement of the tool 10, the longer tether22 will also be tightened to increase the rearwardly-directed pullingforce on the bullet 16 if this is necessary.

It will be appreciated, of course, that a single tether, such as thetether 21, connected eccentrically to the bullet 16 would provide thecombined rotative and rearward movements of the bullet. Such a singletether will, however, most likely unfavorably affect the flight of thebullet 16 as it is impelled against an earth formation. Thus, to avoidsuch undesirable effects as well as to provide a more-secure connectionbetween the body 14 and bullet 16, two tethers as at 21 and 22 arepreferred. Although the type of bullet as well as its size will havesome influence upon choosing the difference in lengths of the twotethers 21 and 22, it has been found that for typical bullets such asthose shown in the aforementioned patents, a difference of only about%-inch in the efiective lengths of the two tethers will be sufiicientfor the purposes of the present invention. Thus, a partial rotation ofthe bullet 16 will be made, which, if necessary to complete thewithdrawal, will be quickly followed by equal pulls on opposite sides ofthe bullet once the longer tether 22 tightens.

Accordingly, it will be appreciated that by employing the principles ofthe present invention, coring bullets may now be more-reliably withdrawnfrom earth formations to achieve a significantly higher rate of recoverythan has been possible heretofore. By at least partially rotating thebullet as it is pulled rearwardly, it has been found that even atightly-embedded bullet will usually be loosened and withdrawn moreeasily from an earth formation. In the preferred manner of accomplishingthis, the otherwise typical tethering cables are made of slightlydifferent effective lengths so that longitudinal movements of thesample-taking tool will initially tighten only the shorter tether topartially rotate the bullet and begin withdrawing it. Then, if thebullet has not yet been completely withdrawn, once the longer tetheringcable also becomes taut, the two cables will pull equally on oppositesides of the bullet to complete the retraction of the bullet from theearth formation.

While a particular embodiment of the present invention has been shownand described, it is apparent that changes and modifications may be madewithout departing from this invention in its broader aspects; and,therefore, the aim in the appended claims is to cover all such changesand modifications as fall within the true spirit and scope of thisinvention.

What is claimed is:

1. A method for obtaining a sample of an earth formation traversed by awell bore and comprising the steps of: positioning a tubularformation-coring bullet in a well bore adjacent to an earth formationfrom which a sample is to be taken so that the longitudinal axis of saidbullet intersects the formation; impelling said bullet forwardly alongits said axis into the earth formation to at least partially embed theforward portion of said bullet therein and force a portion of the earthformation into said bullet; turning said bullet about its saidlongitudinal axis to loosen the embedded forward portion of said bulletin relation to the earth formation thereabout; and pulling said bulletrearwardly to withdraw said embedded forward portion thereof from theearth formation.

2. The method of claim 1 wherein said turning and pulling steps are inconjunction with one another.

3. The method of claim 1 wherein said turning step rotates said bulletonly a portion of a complete revolution.

4. A method for obtaining a sample of an earth formation traversed by awell bore and comprising the steps of: positioning a tubularformation-coring bullet in a well bore adjacent to an earth formationfrom which a sample is to be taken so that the longitudinal axis of saidbullet intersects the formation; impelling said bullet forwardly alongits said axis into the earth formation to at least partially embed theforward portion of said bullet therein and force a portion of the earthformation into said bullet; pulling in a generally-reverse direction onone side of said bullet to at least partially twist said bullet aboutits said longitudinal axis and loosen said bullet in relation to theearth formation as said bullet is being retracted therefrom.

5. The method of claim 4 further including the subsequent step of:pulling in a generally-reverse direction on the other side of saidbullet to augment the retraction thereof from the earth formation.

6. Apparatus adapted for obtaining a sample of an earth formationtraversed by a well bore and comprising: a support adapted forsuspension in a well bore; a tubular coring bullet on said support andhaving a longitudinal bore terminating at an opening in the forward endof said bullet and formation-cutting means adjacent to said forward endthereof; and means connecting said bullet to said support includingfirst and second flexible members of unequal length respectively securedto said support and to circumferentially-spaced portions of said bullet.

7. The apparatus of claim 6 further including: means operable forlongitudinally impelling said bullet forwardly against an earthformation with sufficient force to cut away a portion of such aformation.

8. The apparatus of claim 6 further including: explosive means adaptedfor longitudinally impelling said bullet forwardly against an earthformation with sufficient force to cut away a portion of such aformation;

and means selectively operable from the surface for detonating saidexplosive means.

9. Formation-sampling apparatus comprising: a support adapted forsuspension in a well bore; formationsampling means including a tubularcoring bullet on said support and having a longitudinal bore terminatingat an opening in the forward end of said bullet and formationcuttingmeans adjacent to said forward end thereof adapted for cutting away aportion of such a formation; and means connected to said bullet and saidsupport and responsive to longitudinal movement of said support inrelation to a well bore for at least partially rotating said bulletabout its said longitudinal axis and retracting said bullet from anearth formation from which a portion has been cut away by saidformation-cutting means.

10. The apparatus of claim 9 wherein said movementresponsive rotatingand retracting means include a flexible member respectively secured tosaid support and to an eccentrically-located portion of said bullet.

11. The apparatus of claim 9 wherein said movementresponsive rotatingand retracting means include first and second flexible members ofunequal length respectively secured to said support and tocircLunferentially-spaced portions of said bullet.

12. Apparatus adapted for obtaining a sample of an earth formationtraversed by a well bore and comprising: a support adapted forsuspension in a well bore and having at least one chamber thereindefined about a lateral axis and with an opening on one side of saidsupport; formation-sampling means on said support and including acylindrical coring bullet coaxially disposed in said lateral chamber andhaving a forward end projecting from said chamber opening adapted to beimpelled against an earth formation; and means connecting said bullet tosaid support and responsive only to longitudinal movement of saidsupport in relation to a well bore after said bullet has been impelledagainst an earth formation for imparting a force to said bullet tendingto at least partially turn said bullet about said lateral axis andretract said bullet from an earth formation.

13. The apparatus of claim 12 wherein said connecting means includefirst and second flexible members of unequal length respectively securedto said support and to circumferentially-spaced portions of said bullet.

14. The apparatus of claim 12 wherein said formation-sampling meansinclude explosive means in said lateral chamber adapted for axiallyimpelling said bullet forwardly against an earth formation withsufiicient force to cut away a portion of such a formation; and meansselectively operable from the surface for detonating said explosivemeans.

15. The apparatus of claim 14 wherein said connecting means includefirst and second flexible members of unequal length respectively securedto said support and to circumferentially-spaced portions of said bullet.

References Cited UNITED STATES PATENTS 2,055,506 9/ 1936 Schlumberger 42,944,791 7/1960 Le Bus 175--4 3,220,493 11/1965 Urbanosky 175 -43,280,922 10/ 1966 Bannister 175-4 DAVID H. BROWN Primary Examiner

